Organelle Genomes of Thismia angustimitra Reveal Evidence of Horizontal Gene Transfer

Researchers Gitte Petersen and Henrik Ærenlund Pedersen have presented complete organelle genome data from the mycoheterotrophic plant Thismia angustimitra, identifying evidence that suggests the occurrence of horizontal gene transfer alongside extensive plastome reduction. The research provides complete plastome and mitogenome sequences for an organism representing a fourth clade of mycoheterotrophic plants. Prior to this study, data regarding mycoheterotrophs have remained scarce, with complete mitochondrial genomes known from only three of the ten recognized clades of mycoheterotrophic plants.

The plastome of Thismia angustimitra was found to be 18,215 base pairs in length, reflecting a much reduced structure that includes only a few genes. This condition corresponds directly to established evolutionary trends in non-photosynthetic flora, where plastome degradation and reduced or lost photosynthesis are well-known to go hand in hand. In terms of plastome evolution, research indicates little if any difference between mycoheterotrophic parasites and haustorial parasites. Accordingly, the authors reported that the highly reduced 18,215 base pair plastome of Thismia angustimitra fits completely into the general picture of plastome degradation characteristically observed in heterotrophic plants.

In contrast to plastomes, plant mitochondrial genomes generally appear far less affected by a heterotrophic lifestyle, though certain exceptions occur. In contrast to the uniform patterns seen in plastome evolution, mitochondrial genome evolution may differ between mycoheterotrophic and haustorial parasites, particularly regarding the occurrence of horizontal gene transfer. Investigation of the Thismia angustimitra mitogenome revealed a multicircular architecture consisting of 22 chromosomes with an aggregate length of 422,400 base pairs. In many aspects, the organelle appears unaffected by the heterotrophic lifestyle: its gene content is normal, and its pattern of RNA editing is likewise normal. However, the mitogenome contains only few repeats, and its recombinational activity was determined to be limited and unusually low.

To investigate the potential presence of foreign genetic material within the organelle, the researchers conducted a search across the mitogenome, which did not reveal any fungal sequences. The overall content of plastid DNA inside the mitogenome was also found to be low. Among the identified plastid inserts, just a few appear to have originated through intracellular transfer, whereas other plastid-derived segments most likely stem from horizontal gene transfer. In addition, the researchers found that a large proportion of the mitogenome’s intergenic DNA exhibits sequence similarity to distantly related angiosperms. Analysis of the synteny patterns within these intergenic sequences indicates that horizontal transfer events may happen in either direction between the lineages.

The findings illustrate that even though the mitogenome of Thismia angustimitra appears unaffected by its heterotrophic habit across several baseline metrics, it displays unusually low recombinational activity alongside evidence suggesting horizontal gene transfer. The researchers concluded that finding evidence suggesting horizontal gene transfer in Thismia angustimitra indicates that this transfer phenomenon may be far more common among mycoheterotrophic plants than previously thought.

Subject of Research: Organelle genome characterization and horizontal gene transfer in Thismia angustimitra

Article Title: Characterization of the organelle genomes of mycoheterotrophic Thismia angustimitra and evidence suggesting horizontal gene transfer

Article References: Petersen, G., & Pedersen, H. Æ. (2026). Characterization of the organelle genomes of mycoheterotrophic Thismia angustimitra and evidence suggesting horizontal gene transfer. BMC Genomics, 27(1), Article 923. https://doi.org/10.1186/s12864-026-13542-9

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13542-9

Keywords: Thismia angustimitra, organelle genomes, mitogenome, plastome, horizontal gene transfer, mycoheterotrophy, plant genomics, recombinational activity, Characterization, organelle, genomes, mycoheterotrophic